1. Field of the Invention
The present invention relates generally to a method and apparatus for safely performing spray coating of a refractory material onto a refractory construction. More specifically, the invention relates to a safely and effectively repairing refractory constructions, such as coke ovens, kilns, furnaces and so forth. Further particularly, the invention relates to a spray coating technic avoiding danger in spray coating of the refractory material containing fine particles of powder state combusible metal.
2. Description of the Background Art
Coke ovens, kilns, furnaces employ refractory linings for constituting refractory constructions so as to allow substantially high temperature operations. Such refractory linings thus subject substantially high temperature for a long period of time to cause hot tear, spalling, formation of defect, crack and so forth. As is well known, the coke oven and some kind of furnaces, such as brust furnace, have to be in operation continuously throughout their lives. Accordingly, repair of such hot tears, spalling, defects, cracks and so forth is to be preformed without stopping the operation.
Conventionally, repairing operations for the refractory linings have been taken place by way of spray coating. Such spray coating process has been disclosed in the Japanese Patent Second (examined) Publication (Tokko) Showa 49-46364. In the disclosed process, a refractory material is selected to have same composition to that of the refractory lining to be repaired. The refractory material is mixed with a certain amount of fine particle of powder state combusible metal. In the spray coating operation, heat generated by combustion of the metal powder utilized for melting or half-melting the refractory material and for adhering the refractory material onto the refractory lining. At the same time, the metal oxide formed as a resultant of combustion also serves as refractory material.
In such a conventional spray coating process, it is considered that a caloric value required for performing spray coating of refractory material for repairing refractory linings is in a range of 5000 kcal/kg to 8000 kcal/kg, as recited in "Spray Coating Repair of Coke Oven" (Seitetsu Kenkyu Vol. No. 305), published on 1981, and "Development pf Spray Coating Apparatus and Study of Spray Coating Condition" ("Iron and Steel" No. 4, Vol. No. 169), 1983. Whereas the caloric value may be generated according to the process recited in the afore-mentioned publications is in a range of 2000 kcal/kg to 3000 kcal/kg. Though the proposed process includes inclusion of 20 Wt % to 30 Wt % of metal particle in the refractory material in a form a mixture, which metal particle will serves as combustioning medium. However, the caloric value to be generated by the proposed process is too small to melt or half-melt the refractory materals to be injected onto the surface of the refractory lining. This degrades adherence ability of the refractory material onto the reflactory lining. Furthermore, due to lack of caloric value, formation of satisfactorily high density refractory layer and firm adherence of the formed refractory layer on the reflactory lining have been difficult. It would be possible to increase caloric value of the heat to be generated during combustion by increasing the concentration of the metal powder. However, increasing of the amount of the metal powder concentration apparently cause increasing of the cost required for repairing.
In addition, in the prior proposed process, the metal powder is limited the particle size in diameter to be smaller than 50 .mu.m. The metal powder of the aforementioned limited particle size is carried by oxygen flow. This makes it difficult to practical process due to high combusibility of such fine particle of metal, which causes danger in carrying and back-fire in spray coating process.
Furthermore, since the calory for spray coating is generated only by combustion of the metal particle in the aforementioned prior art, the refractory lining to be repaired cannot be heated in advance of starting spray coating. As a result, the refractory lining to be treated is rapidly heated at a spot. The heating spot of the refractory lining is rapidly cooled when the spray coating operation is terminated. This tends to cause spalling in the refractory construction to be repaired.